The voltage and current output of thin film solar cells, e.g., amorphous silicon solar cells such as those described in U.S. Pat. No. 4,064,521 or screen printed solar cells, may be greatly reduced or completely eliminated by electrical shorts or shunts formed during the fabrication of the solar cell. Electrical shorts occur when there is a pinhole in the semiconductor body and the front and back electrodes are touching. A shunt is the loss of charge in the semiconductor body due to imperfect barrier formation or the formation of an ohmic contact by a high-work function metal rather than a Schottky barrier formation. The problems of solar cell defects which cause shorts or shunts greatly increase with increasing solar cell size.
If large area solar cells are to be economically feasible, then methods to either eliminate these shorts and shunts during fabrication or a method of removing the defects after processing must be developed. Since the former will require facilities and processing conditions which greatly increase the cost of solar cells, the latter, a method of removing shorts and shunts, is preferable. The present process for removal of a defect in solar cells made from gallium arsenide, cadmium telluride, single crystal or amorphous silicon and the like, requires the etching out of the defect in the solar cell. Attempts made to remove the defects by the application of a reverse bias voltage tended to increase the incidence of shorts and shunts in the solar cell.
Solar cells incorporating a thick film metal cermet are disclosed in copending application Ser. No. 899,564, filed Apr. 24, 1978. Cermets are composite materials consisting of finely dispersed mixtures of immiscible metals and insulators. Cermet-containing amorphous silicon solar cells exhibit increased resistance to defects form shorts and shunts in comparison to conventional solar cells. However, cermet solar cells are subject to the same performance degrading effects as conventional solar cells as the cell area increases. Thus, it would be highly desirable to find a method of removing the effect of electrical shorts and shunts created during the fabrication process.